Cam assemblies are known for providing a torque to wind and unwind a cable in a hoist mechanism such as a tire lift carrier. Known cam assemblies include an input shaft that is connectable to a torque providing drive mechanism that rotates the cam assembly. The cam assembly cooperates with a spool to release or wind up the cable, depending on the direction of rotation. In certain situations, such as when the cable is fully unwound from the spool or when a spare tire is completely in a storage position with respect to an underside of the vehicle, over-torquing of the cam assembly can occur, leading to damage to the drive mechanism or to the hoist mechanism. Known cam assemblies are disadvantageous as there is no means for preventing or alerting a user of the cam assembly over-torquing.
One proposed cam assembly has attempted to overcome the over-torquing problem by incorporating a spring loaded clutch plate that cooperates with an input shaft, a cup-shaped plate, and a cam for winding and unwinding cable. The clutch plate has three rectangular apertures positioned radially and equidistantly from the center of the plate. Each rectangular aperture has a center radial passage that opens from a radially outermost portion of the outer circumference of the plate, the passages being defined by adjacent arcuate edge portions. The clutch plate retains three springs, each having a short outwardly extending central portion. The springs are positioned along the outer circumference of the clutch plate, whereby ends of the springs extend within the radial passages and engage with the rectangular apertures to retain the springs on the clutch plate. The clutch plate is positioned within the cup-shaped plate such that the central portion extends within notches formed within the cup-shaped plate. As the shaft is rotated, the clutch plate rotates due to the central portion's engagement with the notches, thereby rotating the cup-shaped plate and cam relative to the shaft. If the rotation of the cam assembly experiences a resistance that is greater than the maximum limit prescribed by the springs, the central portion of the springs smoothly displace in and out of the plate notches.
One significant drawback to such a cam assembly is the number of components and the machining requirements of the clutch plate. By including so many components, the likelihood of damage to the cam assembly is increased. Further, the assembly time is significantly increased, as are manufacturing costs. In addition, there is no indicator means to alert a user when the cam assembly has exceeded a maximum resistance limit.
Therefore, there exists a need for cam assembly that protects against over-torque with a reduced number of components and further includes an indicator to alert a user when the cam assembly has exceed a maximum level of resistance.